The control valve with pneumatic actuator is the final control element of the absolute majority of the flow meshes. Even with the increasingly intensive and extensive use of electronic instrumentation, the valve with pneumatic actuator is still the most applied, simpler, more reliable, economical and efficient final element than the valve with electronic actuator, (Ribeiro, 1999).
The pressure control valve is a device having as function to relief the pressure exceeded of a system, either be pipes that transport or store a liquid or a gas under high pressures. The objective of installing a security valve is to protect the system from excessive pressure effects, where there is risk of damaging the system, risk of explosions and life threatening. This protection occurs when a valve is able to discharge a certain flow rate enough to reduce the pressure of a system to a certain level of safety.
It is a device very widely applied in the industry in general, however there is no model on the market specifically designed for application in blood flow control, i.e., it keeps these characteristics and is free from aggression to blood.
Several advisory devices used in extracorporeal circulation (CEC) require a component with this protection function. In CEC, blood is pumped at flows greater than 5 liters per minute. These flows generate high pressures, being able to exceed 300 mmHg, which generates risks of damages to devices such as hemoconcentrators and hemofilters. The hemoconcentrator is a device used in CEC with the function of removing blood liquids, being formed by a bundle of hollow and microporous fibers with walls of microscopic thickness. For example, polysulfone fiber has a thickness of 30 μm and has a low-pressure tolerance. Once the pressure tolerance threshold is exceeded, the fiber may rupture and leak the blood in its interior.
Thus, in order to design a valve model that could provide protection to the hemoconcentrator and, at the same time, would not be aggressive to the blood elements noted from the blood, notably for CEC application, the membrane valve for controlling flow and pressure relief was developed.